The role of hormone binding in the cold suppression of hormone stimulation of the pituitary, thyroid, and testis of the turtle.
The ability of hormones to bind to their functional receptors on turtle (Pseudemys scripta) endocrine target tissues in the cold was tested by treating tissues with secretagogues at low temperatures (5-15 degrees) and then following subsequent target stimulation in the absence of secretagogue at a warm temperature (28 degrees). Administration of thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone, and growth hormone-releasing hormone to pituitaries at low temperatures (20 degrees or below) suppressed responses in growth hormone (GH) and thyrotropin (TSH) secretion and there was little or no response in pituitaries subsequent to warming. In contrast, gonadotropin-releasing hormone treatment of pituitaries, TSH treatment of thyroid glands, and gonadotropin (FSH and LH) treatment of testes in the cold (down to 5 degrees) was followed by a large response in the target glands (secretion of LH, thyroxine, and testosterone (T), respectively) following warming. Additional studies with FSH and LH showed that these hormones can bind to testes rapidly (within 5 min) at low temperatures where no acute response is observed, although the dose sensitivity and the extent of this priming in the cold are less than at warm temperatures. Thus, postreceptor events may be more important than binding per se for temperature effects on hormone responses of tissues, but even this component of cell function varies among tissues. The effects of a receptor-independent secretagogue (tetraethylammonium chloride), which causes cell depolarization by blocking K+ efflux, were also blocked at low temperatures in thyrotropes and somatotropes but not in gonadotropes. Rapid depressions in TSH and GH secretions following cooling of TRH-stimulated pituitaries and of T secretion in LH-stimulated testes provide further evidence for cold sensitivity of postreceptor processes in these tissues.
Licht
P
P
Department of Integrative Biology, University of California, Berkeley 94720.
Pavgi
S
S
Denver
R J
RJ
D000818:Animals; D003080:Cold Temperature; D046508:Culture Techniques; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology; D013006:Growth Hormone / Q000378:metabolism; D006728:Hormones / Q000378:metabolism / Q000502:physiology*; D006358:Hot Temperature; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism*; D013737:Testis / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism / Q000502:physiology; D013974:Thyroxine / Q000378:metabolism; D014426:Turtles / Q000378:metabolism / Q000502:physiology*
D006728:Hormones; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; D013972:Thyrotropin; D013006:Growth Hormone; D013974:Thyroxine